But as the presidential marathon evolves into a sprint, the story line remains simple: Gore is the overwhelming favorite to win the Democratic nomination, and Bush is the overwhelming favorite in the GOP.

That hasn't changed after more than a year of campaigning. What is different is the credibility given to the challengers and the vulnerability associated with the front-runners. Gore and Bush have each had trouble maintaining enthusiasm among their supporters. Bradley and McCain, meanwhile, each have raised substantial sums of money and, playing on their insurgent appeal, have pulled into the lead in New Hampshire polls.

Most Americans have just begun to tune into a race that already has seen three credible candidates drop out and tens of millions of dollars spent. But the whirl of activity in Iowa and New Hampshire -- frequent rallies, back-to-back political commercials, nightly candidate debates -- soon will spread to dozens of states.

In the 43 days between the Iowa caucus (January 24) and the California primary (March 7), 27 states will hold caucuses or primaries, and about half of the delegates to the nominating conventions will be selected. It is hard to imagine a scenario in which the contests are not decided by mid-March, and it could end many weeks sooner.

Here is a look at the state of the campaign in the final weeks before the first ballots are cast.

A year ago, the vice president looked invincible within his own party. A lineup of potential challengers, including Minnesota Sen. Paul Wellstone, Nebraska Sen. Bob Kerrey and the Rev. Jesse Jackson, decided not to enter the race, and the entire Democratic Party establishment lined up on Gore's side.

But his campaign stumbled after a series of miscues. His stump speech left supporters uninspired. His campaign bled money to high- priced consultants like author Naomi Wolfe, who helped advise Gore on how to come across as an "alpha male."

As Bradley appealed to the party's liberal base -- with positions on gun control, health care and campaign finance reform -- Gore watched his double-digit lead evaporate in New Hampshire.

Bradley has raised nearly as much money as Gore (about $26 million) and has spent less, giving him more money for the final push. And despite an 18-year career as a senator, Bradley has positioned himself as a straight-talking Washington outsider battling the entrenched powers whose support Gore has monopolized.

"When I hear you talk, Al, it reminds me of a Washington bunker. And I think you're in a Washington bunker," Bradley said last week at a debate in New Hampshire.

"And I can understand why you're in a bunker," he said. "I mean, there was Gingrich. There were the fund-raising scandals. There was the impeachment problem. And I think that the major objective in the last several years in the White House has been political survival. I understand that. But the reality is, the Democratic Party shouldn't be in the Washington bunker with you."

Gore has fought back by distancing himself from President Clinton, moving his campaign headquarters from Washington to Tennessee and telling anyone who will listen that he is better equipped to roll up his sleeves and carry out the Democratic agenda.

"The presidency is not an academic exercise," Gore said in the same debate. "It's not an extended seminar on theory. It has to be a daily fight for the best interests of the American people."

Although the New Hampshire race is tight, Gore leads Bradley nationwide by nearly a 2-to-1 margin. And although the vice president has less cash on hand, he does have some institutional advantages.

It takes 2,169 delegates to clinch the Democratic nomination, about 800 of whom are party leaders and members of Congress known as super delegates. Gore already has endorsements from 500 of those super delegates. This means Bradley needs to win nearly 60 percent of delegates in caucuses and primaries to capture the nomination.

California might prove pivotal in the Democratic race. After the New Hampshire primary February 1, Democrats have no further contests until March 7, when California (where Gore leads), New York (where Bradley leads), and 13 other states hold votes.

A Bradley victory in New Hampshire and California might neutralize Gore's institutional advantages and make a race of it. A Gore victory in New Hampshire could mortally wound Bradley's hopes, and a Gore victory in California would make it difficult for Bradley to catch up.

REPUBLICANS

The Bush campaign has insisted all along that its bubble of popularity wouldn't last forever. After raising a record $70 million and building a huge lead in the polls, Bush watched as John McCain surged ahead in New Hampshire.

Like Bradley, McCain has played upon his credibility and his maverick stances on issues such as campaign finance reform to promote himself as a political outsider, despite an 18-year career in Washington.

His accessibility and bluntness with reporters has made him a hit with the media, earning him a lot of favorable press and making him popular with New Hampshire voters who cherish a hands-on relationship with candidates.

The big question for McCain is what will happen if he wins New Hampshire. The campaign readily admits that it cannot compete with Bush's resources and national organization.

Sensing an embarrassing defeat in Iowa, McCain chose not to compete there. But his campaign hopes early victories in New Hampshire (February 1), South Carolina (February 19) and Arizona (February 22) will reshuffle a race built on the presumption that Bush is the party's most electable candidate.

"If John McCain breaks out, he's going to ride a news media tidal wave all the way to California," said Dan Schnur, his communications director. "This is going to be the ultimate test of message and momentum versus organization and endorsements."

The Bush camp says even a series of McCain victories could not derail its grip on the nomination.

"If you want to be a candidate of a national party, you have to be able to demonstrate you are capable of winning everywhere," said Carl Rove, Bush's chief strategist.

And so Bush has organizations in 50 states, the District of Columbia, Puerto Rico, the Virgin Islands, Guam and American Samoa. In California, where McCain has a couple of staffers, Bush already has divided the state into 18 districts and named chairs and co-chairs for each. Their headquarters in Los Angeles soon will be augmented by another in Orange County.

Privately, McCain's aides admit that if he does not win in New Hampshire and South Carolina, the campaign will be over.

But there can be no doubt that the race has tightened. When Bush made his first trip to New Hampshire in June, he took off the first Sunday, saying he refused to campaign seven days a week and that he needed to preserve one day for family and rest.

However, yesterday, Bush had two stops on his schedule, including a youth forum in Manchester and a campaign dinner in Durham.

The Republican field also includes millionaire magazine publisher Steve Forbes, Utah Sen. Orrin Hatch, conservative activist Gary Bauer and former Reagan administration official Alan Keyes. Although Forbes has been running for president since 1994 -- and by some estimates has spent close to $100 million of his own money -- none has shown any base of support in the polls.

TONIGHT'S DEBATE

The six Republican presidential candidates will debate tonight: -- Where: Calvin
College
, Grand Rapids, Mich. -- When: 4 to 5:30 p.m. PST. -- Coverage: Live on MSNBC and National Public Radio.